This invention relates to an undercut beneath the platform of a trailing edge of a turbine blade, wherein the undercut has a shape designed to reduce undesirable stress concentration in the platform.
Turbine blades typically include a platform, with an airfoil extending radially outward from the platform. The airfoil and platform are exposed to thermal stress as they come into contact with heated gasses passing through the turbine. The thermal stresses, as well as the stress caused by the spinning of the turbine blade about the shaft of the gas turbine, create stresses in the turbine blade that can lead to crack formation and propagation in the turbine blade at or near the airfoil/platform interface.
One method of reducing this type of stress is by incorporating an undercut at a trailing edge of the platform under the airfoil. Prior art undercut designs included curves having a single radius, whether used alone, or in combination with other curves having a single radius. While the known undercuts do reduce stress concentrations, single-radius curves leave highly stressed areas adjacent the portion of the radius merging into the platform, and combinations of single radius curves create non-uniform stresses portions of the undercut.